1. Field
Example embodiments relate to magnetic memory devices and methods of operating the same.
2. Description of the Related Art
Magnetic random access memories (MRAMs) are memory devices that store data by using a variation in resistance of a magnetic tunneling junction (MTJ) element. The resistance of the MTJ element varies according to a magnetization direction of a free layer. That is, when the magnetization direction of the free layer is the same as a magnetization direction of a pinned layer, the MTJ element has low resistance. When the magnetization direction of the free layer is opposite to the magnetization direction of the pinned layer, the MTJ element has high resistance. A case where the MTJ element has the low resistance may correspond to data ‘0’, and a case where the MTJ element has the high resistance may correspond to data ‘1’. Because MRAMs are non-volatile, capable of high speed operations and have high endurance, MRAMs have gained attention as one of the next generation non-volatile memory devices.
A typical MRAM includes an MTJ element having a horizontal magnetization, and uses a digit line and a bit line to switch a magnetization direction of a free layer. Such an MRAM uses an MTJ element having a horizontal magnetization, and also has a relatively complicated structure, and accordingly, it is difficult to realize high-densification.
In the case of a spin transfer torque magnetic random access memory (STT-MRAM) that does not use a digit line, a magnetization direction of a free layer is switched by using a spin torque that occurs due to a current flowing through an MTJ element. However, to secure data retention characteristics of a free layer, a material with high magnetic anisotropy energy is used as a free layer material. When a material having a high magnetic anisotropy is used for the free layer material, an amount of the current (that is, a switching current) required to switch a magnetization direction of the free layer increases. Accordingly, a large-size cell transistor is required for supplying the switching current. In addition, in the case of the STT-MRAM, a writing current needs to be repeatedly provided to the MTJ element. Accordingly, problems related to endurance and reliability of a tunneling layer interposed between a free layer and a pinned layer of an MTJ element may occur.